Abstract :
This project introduces a new class of solutions for collective decision-making problems under uncertainty such as the climate crisis, health emergencies such as COVID-19, and the economic impacts of technological disruptions. In particular, it examines the relationship between preference aggregation across individuals in collective decisions and across possible events for a single individual who does not know which event will occur. More precisely, we assume that agents have a utility for each option, which may vary from one event to another. Agents can aggregate their utilities across different events into a single utility using an aggregation function. The objective is to explore the connection between how utilities are aggregated across agents for a given option in a given event and how they are aggregated across events for a given option and a given agent. For example, if a couple consistently chooses to go to a restaurant regardless of the weather, the collective choice method should also recommend going to the restaurant when considering their overall preferences before knowing the weather. To achieve this, we adopt an axiomatic approach centered on a consistency principle: if the same option is socially chosen for two distinct utility profiles corresponding to two distinct events, then this option should also be chosen for the utility profile resulting from their aggregation. This axiom, combined with Unanimity, Anonymity, and Neutrality, ensures that each agent’s preferences across different events are aggregated in the same manner as the preferences of different agents within the same event. Furthermore, by incorporating additional axioms and an algebraic approach, we characterize various interesting solutions.